New asymmetric polyamides



United States Patent NEW ASYMMETRIC POLYAMIDES Joseph A. Blanchette, East Longmeadow, Mass, assignor to Monsanto Chemical Company, St. Louis, Mo.,' a corporation of Delaware N0 Drawing. Filed Sept. 23, 1957, Ser. No. 685,432

4 Claims. (Cl. 260-78) This invention relates to novel synthetic linear polyamides. More particularly, this invention relates to polyamides containing asymmetric carbon atoms.

A wide variety of polyamides are described in the art, ranging from soft and tacky resins to hard and highmelting resins. Such resins have found many important applications, e.g., as synthetic fibers, coatings, wearresistant machine gears, etc.

Now it is an object of this invention to provide novel polyamides containing asymmetric carbon atoms.

Another object is to provide highly crystalline polyamides possessedof high melting temperatures, good solvent resistance and superior strength.

These and other objects are attained by the condensation polymerization of asymmetric dicarboxylic acids with heterocyclic diamines under sub-atmospheric pressures and at elevated temperatures to produceresinous polyamides having a plurality of recurring units corresponding to the general formula:

wherein x is an integer of from 1 to 5, y is'an integer of from 1 to 9, z is an integer of from 2 to 9 and m is an integer of at least 10.

The following examples are given'in illustration of the invention and are not intended as limitations thereof.

Example I 8.6 grams (0.1 mol) of piperazine and 12.5 grams (0.1 mol) of levo-malic acid are charged to a vacuum vessel and heated at 120 C, under a 2 0 mm. of Hg vacuum for about 6 hours. The vacuum then is increased to about 100 mm. of Hg and heating is continued at 120 C. for about another 2 hours or until the evolution of water vapor ceases. The resulting resinous solid is dissolved in tetrahydrofuran and precipitated from water. Filtration and drying yields a transparent, crystalline polymer.

Example II 7.2 grams (0.1 mol) of tetrahydro-l,3-diazole and 16.2 grams (0.1 mol) of alpha-hydroxy-butane-1,4-dicarboxylic acid are charged to a vacuum vessel and heated at 120 C. under a 100 mm. of Hg vacuum for about 8 hours or until the evolution of water vapor ceases. The resulting resinous solid is dissolved in tetrahydrofuran and precipitated from water. Filtration and drying yields a crystalline polymer.

As previously mentioned, the resinous polyamides of this invention are the products of the condensation polymerization of substantially equimolar quantities of asymmetric dicarboxylic acids and certain diamines. The asymmetric dicarboxylic acids so employed correspond to the general formula:

tice of this invention. Therefore, this invention encompasses the use of. either the dextroor levostereoisomers,

or the dextro-levo mixtures thereof, of malic acid, alphahydroxy-propane-1,3-dicarboxylic acid, alpha-hydroxybutane-1,4-dicarboxylic acid, alpha-hydroxy-pentane-l,5-

dicarboxylic acid, and alpha-hydroxy hexane-l,6-dicarboxylic acid and mixtures thereof.

The diamines employed in this invention are secondary heterocyclic. diamines corresponding to the general formula:

(Clilrla wherein y is an integer of from 1 to 9 and z is an integer of from 2 to 9. Examples of such heterocyclic diamines include piperazine and the other hexahydro diazines, the tetrahydro diazoles, etc.

'The novel resinous polyamides of this invention are I prepared from substantially equimolar proportions of the I 'foregoing asymmetric dicarboxylic acids and secondary diamines, many of which are solids at room temperature.

Condensation and polymerization may be accomplished" in the absence of solvents by maintaining the reactants in a liquid state, i.e., at a temperature above the liquefaction temperature of the highest melting component.

Preferably, since the rates of the condensation reaction and of the polymerization 'are proportional to the temperature of the reaction system, reaction temperatures slightly below, i.e., 5 to 20 C. below, the boiling temperature of the lowest boiling components are employed. Water formed during the reaction must be removed from the reaction system if high polyamide yields are to be obtained. The use of a water immiscible solvent, e.g., benzene, for the reactants and the polyamide product is one way of achieving this result. However, the water may also be removed from solvent-free reaction systems by vacuum distillation techniques. Generally, shorter reaction cycles and better products are obtained when the reaction is run under sub-atmospheric pressures, i.e, 15-150 mm. of mercury vacuum.

The novel polyamides of this invention are prepared in degrees of polymerization of at least 10 units; those polyamides having from 20 to units being especially preferred. As initially obtained, the resinous product is contaminated with small amounts of residual dicarboxylic acid and diamine. To purify, the solid product is first dissolved in organic solvents such as tetrahydrofuran, dimethylformamide, etc., and then is re-precipitated by adding this solution to a large excess of a liquid which is (1) miscible with the solvent, (2) a solvent for the di' carboxylic acid and diamine contaminants and (3) is a nonsolvent for the polyamide. Examples of such liquids are methanol and water.

The polyamides of this invention are new and highly oriented linear resins possessed of a high degree of crystallinity. They are insoluble in the lower solvents, i.e., alcohols, ethers, ketones, etc., are high melting and have excellent tensile strength.

These polyamides may be used per se or they may be modified by the incorporation of conventional additives such as plasticizers, dyes, etc. They may also be used Patented Nov. 8, 1960 3-". in combinationwithotherresins... e23".v lky r yl r diene polymers, etc.

Films may easily be prepared from the lower molecular; weight polyamides by; conventional A film casting tech?- niques; Such films are especially useful in packaging applications; e;g.-,, meats, foodstufis, clothing, etc. An. exampleof filmpreparation is-as follows.

Example. III

1 Ten grams of thepolyamide prepared in Example I...

is dissolved in 100 ml. of tetrahydrofuran'together with,- 0.5 gram of. a polyethylene glycol having. an average, molecular weightof about 400 as. plasticizer. After thorough mixing, the sirupy mixture is poured onto a glass plate as a uniform-0.010" film. The plate is dried in an oven at 80 C. for2 minutes after which the filmv is peeled." The resultant transparent film is insoluble; in common solvents, is highly flexible and possesses high strength.

'Fibers for textiles, brush bristles, etc. may be similarly prepared by dissolving intermediate molecular weight polyamides in, for example, tetrahydrofuran, and spinning the solution into a water bath according to conventional practices. These polyamides are also usefulas molding and coating; compositions,

It is obvious that many variations may be made in;the product and processes of this invention without departing from the spirit and scope thereof.

What is claimed is:

1. A resinous polyamide containing asymmetric carbon atoms and consisting of a plurality of recurring unitscorresponding to the general formula;

wherein-x isan.integer.of-from 1to 5, y is-;an-integer of from 1 to 9, z is an integer of from 2 to 9, and m is an integer of from to 70.

2. A resinous polyamide containing asymmetriccar- 4. a. atoms. dconsistingpfa plurality. f. recnrringnnjta. of the formula:

c OH o (CH2):\ [c t cn. t N

wherein m is an. integerof from .10 to. 70.

3. A processforpreparinga resinous polyamide.containing. asymmetric-carbon atoms. and consisting of l a plu- 0 rality of recurring structuralunits, correspondingtothe general formula:

the-boiling temperature. Of:th 1OWCSt boiling componentg saidasymmetric digarb'oxylic acid corresponding, to the,

general formula:

11ooc- :i- -(c.n=)ae0.0H.

H and'said heterocyclic diamine corresponding tothe general' formula:

HN :NH"

(011:) wherein in eachof; the.above-formulae, x is anintcgcrof from 1 to 5, y is an integer. of from 1 to 9, z is an integer of from 2.109 and. m is an integ er-of from 10 to 70.

4. A processes in claim 3 wherein the asymmetric dicarboxylicacid is-malic acid and the heterocyclic diamine is piperazine.

References-Cited in the file-of this patent UNITED STATES PATENTS ,1 3, Carothers Mar. 7; 1939 

1. A RESINOUS POLYAMIDE CONTAINING ASYMMETRIC CARBON ATOMS AND CONSISTING OF A PLURALITY OF RECURRING UNITS CORRESPONDING TO THE GENERAL FORMULA: 